Summary
A monospecific antiserum against factor X was prepared in rabbits. The antiserum precipitated factor X in human plasma and serum and monkey serum. The antiserum was used to :
1. demonstrate the presence of factor X precursor in blood from patients under anticoagulant therapy,
2. produce an artificial factor X deficiency substrate useful for testing factor X,
3. study the species specificity of factor X from various common laboratory mammals.
